| Quantum information storage, a hot research of the quantum information science in recent years, can be used in the research of quantum repeater, quantum computation, etc. As a good storage medium, atomic ensemble has long coherence time in ground state.To put the entangled light source be storaged in atomic-ensemble has become the focus of the science and technology at home and abroad.The most mature and most widely technology of the experiment on entangled light source is the spontaneous parametric down conversion process. The photon pairs have high correlation in aspects such as time, space, energy, polarization, which can be applied to the preparation of quantum entanglement, long-distance quantum communication and quantum teleportation, etc.In general, the line-width of the entangled photon pairs produced by SPDC process lies in the THz magnitude. However, it does not match the atom-ensemble quantum storage, whose band-width is several MHz. In addition, the correlation time of photon pairs is for ps magnitude, so that it is unable to realize the independent interference between entangled light sources for the single photon detectors that used in the experiment is for hundreds of ps.The cavity-enhanced SPDC process can effectively solve this problem. Not only it can enhance the conversion process, but also can effectively narrow the line-width of photon pairs. The main content of this paper is around the cavity-enhanced SPDC process to generate narrow-band photon pairs, which is suit to storage in Rb atoms ensemble. This paper carries out a series of experimental research around this process. The work we have worked out includes aspects as follows:(1) We product the 397.5nm violet light through the study of the frequency doubling 795nm red light, which provides the required pump light source for the SPDC process. In addition, we analyze the various factors that influence the efficiency of frequency-doubling.(2) We study the SPDC process of the type-II PPKTP crystal. Firstly, we work out the single-pass experiment and test the relation between the brightness of the down-converted photon pairs and the pump power inputted. Based on it, we put the SPDC process in a optical resonator and get the narrow-band polarization photon pairs through the enhanced-cavity SPDC process. When the input pump power is for 0.2mW, the relative time of photon pairs we measured is for 14.6ns, the line-width corresponding to is about 15MHz.This paper work provides basis for the next work to realize the narrow-band entangled photon pairs to be stored in the atomic ensemble. |
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